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    2 questions

    2 questions

    New postby mtCDCcb on Tue Feb 14, 2012 5:30 pm

    I am building a new home. I am building in the mountains where there is are harsh winters. I am told the 2006 residential and energy i-codes? apply.
    1) I want to insulate the rafters of my garage with batt insulation (id do it myself). There is no living space above and the garage is unconditioned. If I use batt insulation do I need to vent the rafters, if I do would it just be easier to use spray in insulation?
    2) My kitchen is a the front of the house and I need to vent my kitchen range. I don't want tje vent from my range at the front of the house for aesthetic reasons. I asked the inspector and he said he didn't care where I vented my range. My question is can I join my range with other ducts in the home so it vents out somewhere other than the from of the house?
    Thanks.
    mtCDCcb
     
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    Re: 2 questions

    New postby Jerry Peck - Codeman on Tue Feb 14, 2012 8:42 pm

    mtCDCcb wrote:1) I want to insulate the rafters of my garage with batt insulation (id do it myself). There is no living space above and the garage is unconditioned. If I use batt insulation do I need to vent the rafters, if I do would it just be easier to use spray in insulation?


    There are two types of attics: 1) the standard vented attic with insulation laid against the ceiling and the attic is vented to the required minimum (or greater) requirements; 2) the sealed attic with insulation against the underside of the roof decking and no ventilation - thus it is called a sealed attic.

    With 1), the standard vented attic, the thermoenvelope is the insulated walls and the ceiling. That creates the envelope which encloses the conditioned space. The attic is basically at outside temperature with exceptions for heat gain; the attic is hotter than outside temperature during the summer because the ventilation is not complete and sufficient to ventilate the attic to replicate the outside temperature, and the attic is warmer than the outside temperature during the winter, and colder than the conditioned space within the thermoenvelope below.

    With 2), the sealed attic, the thermoenvelope is the insulated walls and the roof decking. That creates the envelope which encloses the conditioned space. The attic is basically at the same temperature as the conditioned space below, and the attic is considered to be 'conditioned space' for heating/cooling sizing as the ceiling does not act as much of an insulator between the attic and the conditioned space below.

    Saying that you want to 'insulate the rafters' indicates you are thinking of 2), a sealed attic. Batt insulation is not a good choice for that use as most batt insulation you will get will be faced (has a paper or foil facing) and the facing is required to be in substantial contact with building material, i.e., such as laying on the drywall ceiling. This is because the facing will burn. Using 'unfaced' insulation is a way to avoid the problem with leaving the facing exposed, however, unfaced creates other problems.

    Also, the codes basically do not allow fiberglass insulation batts (faced or unfaced) to be installed on the rafters (there are exceptions in the code).

    If you are going to go with 2), the sealed attic, then spray foam insulation is what you want to use. However, the spray foam insulation comes with its own drawbacks, and that is protecting the spray foam insulation from heat and flame, so a thermal barrier and an ignition barrier may need to be installed, of just an ignition barrier - depends on the specific conditions of the attic.

    Is the garage going to have a ceiling, or is the garage going to have open trusses with the 'attic' open all the way to the roof decking?

    Additionally, if you are to insulation the garage attic, you will want to insulate the garage walls and the garage doors.

    I know that I have not answered your questions, and that I have given you a bit to consider, but the answers will help answer the question.

    2) My kitchen is a the front of the house and I need to vent my kitchen range. I don't want tje vent from my range at the front of the house for aesthetic reasons. I asked the inspector and he said he didn't care where I vented my range. My question is can I join my range with other ducts in the home so it vents out somewhere other than the from of the house?


    No, all the exhausts will need to be vented to the outdoors separately.

    Yes, you can vent the exhausts to the outdoors through the sides or back of the house.

    Not sure what "somewhere other than the from of the house" means, but - no, you cannot exhaust into the garage, attic, or crawlspace (if present).
    Jerry Peck - CodeMan
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    Re: 2 questions

    New postby mtCDCcb on Tue Feb 14, 2012 11:33 pm

    meant "front of the house". Basically asking if I could join my range vent in with other ducts and it appears I can not. I am sure my installer is going to want to take the shortest and easiest way which is directly out to the front of the house and I would rather not have this. Seems like it can be vented outside elsewhere, but I must vent it separately

    Where does the code not allow batt insulation for rafters? I would like to show that to my contractor as it was his recommendation.

    So basically I should just spray in the rafter and not vent it (cold roof). This is the way the rest of the home is being done?
    mtCDCcb
     
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    Re: 2 questions

    New postby Jerry Peck - Codeman on Wed Feb 15, 2012 9:16 am

    The exhausts can be vented out anywhere convenient, such as through a gable end, through the roof on the rear faces where they are not seen, etc., but not into the soffit area either. There really is no reason to have the exhaust discharge at the front, and although many contractors go for the shortest and cheapest way, as the buyer you can tell them differently - they may say that there is an extra cost, which would be up to you to accept or not.

    "So basically I should just spray in the rafter and not vent it (cold roof). This is the way the rest of the home is being done?" Correct.

    (bold and underlining are mine)
    - R806.4 Conditioned attic assemblies. Unvented conditioned attic assemblies (spaces between the ceiling joists of the top story and the roof rafters) are permitted under the following conditions:
    - - 1. No interior vapor retarders are installed on the ceiling side (attic floor) of the unvented attic assembly.
    - - 2. An air-impermeable insulation is applied in direct contact to the underside/interior of the structural roof deck. “Air-impermeable” shall be defined by ASTM E 283.
    - - - Exception: In Zones 2B and 3B, insulation is not required to be air impermeable.
    - - 3. In the warm humid locations as defined in Section N1101.2.1:
    - - - 3.1. For asphalt roofing shingles: A 1-perm (5.7 × 10-11 kg/s ⋅ m2 ⋅ Pa) or less vapor retarder (determined using Procedure B of ASTM E 96) is placed to the exterior of the structural roof deck; that is, just above the roof structural sheathing.
    - - - 3.2. For wood shingles and shakes: a minimum continuous 1/4-inch (6 mm) vented air space separates the shingles/shakes and the roofing felt placed over the structural sheathing.
    - - 4. In Zones 3 through 8 as defined in Section N1101.2, sufficient insulation is installed to maintain the monthly average temperature of the condensing surface above 45°F (7°C). The condensing surface is defined as either the structural roof deck or the interior surface of an air-impermeable insulation applied in direct contact with the underside/interior of the structural roof deck. “Air-impermeable” is quantitatively defined by ASTM E 283. For calculation purposes, an interior temperature of 68°F (20°C) is assumed. The exterior temperature is assumed to be the monthly average outside temperature.

    Fiberglass insulation is not An air-impermeable.

    Note that the exception: Exception: In Zones 2B and 3B, insulation is not required to be air impermeable. addresses the following areas only:
    - 2B includes the southern tip of Texas roughly souht of, and to the west of, San Antonio, and, Arizona south of Phoenix
    - 3B includes an area around where Nevada, Utah, and Arizona meet, and, roughly the center third of California south of Redding, and widening to the east roughly at Bakersfield

    If you are outside that area, the exception does not apply.
    Jerry Peck - CodeMan
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    Re: 2 questions

    New postby mtCDCcb on Wed Feb 15, 2012 1:20 pm

    Thanks so much you have been very helpful. Great site.
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